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Vol 104, No 2 (2016)

Optics and Laser Physics

Spin centers in SiC for all-optical nanoscale quantum sensing under ambient conditions

Anisimov A.N., Babunts R.A., Kidalov S.V., Mokhov E.N., Soltamov V.A., Baranov P.G.

Abstract

Level anticrossing (LAC) spectroscopy has been demonstrated on a family of uniaxially oriented spin color centers with S = 3/2 in the ground and excited states in hexagonal 4H-, 6H-, and rhombic 15R-SiC polytypes. It has been shown that these centers exhibit unique characteristics such as optical spin alignment up to the temperatures of 250°C. A sharp variation of the IR photoluminescence intensity in the vicinity of LAC with the record contrast has been observed, which can be used for a purely all-optical sensing of the magnetic field and temperature without applying radiofrequency field. A distinctive feature of the LAC signal is weak dependence on the direction of the magnetic field that allows one to monitor the LAC signals in the nonoriented systems, such as powder of SiC nanocrystals.

JETP Letters. 2016;104(2):82-87
pages 82-87 views

Condensed Matter

Magnetization of Mn1–xFexSi in high magnetic fields up to 50 T: Possible evidence of a field-induced Griffiths phase

Demishev S.V., Vanacken J., Kagan M.Y., Grigoriev S.V., Dyadkin V.A., Chubova N.M., Sluchanko N.E., Lobanova I.I., Glushkov V.V., Huang J., Samarin A.N., Moshchalkov V.V.

Abstract

Magnetic properties of single crystals of Mn1–xFexSi solid solutions with x < 0.2 are investigated by pulsed field technique in magnetic fields up to 50 T. It is shown that magnetization of Mn1–xFexSi in the paramagnetic phase follows power law with the exponents M(B) ~ Bα, which starts above characteristic fields Bc ~ 1.5-7 T depending on the sample composition and lasts up to highest used magnetic field. Analysis of magnetization data including SQUID measurements in magnetic fields below 5 T suggests that this anomalous behavior may be likely attributed to the formation of a field-induced Griffiths phase in the presence of spin-polaron effects.

JETP Letters. 2016;104(2):116-123
pages 116-123 views

Magnetostructural phase transitions in NiO and MnO: Neutron diffraction data

Balagurov A.M., Bobrikov I.A., Sumnikov S.V., Yushankhai V.Y., Mironova-Ulmane N.

Abstract

Structural and magnetic phase transitions in NiO and MnO antiferromagnets have been studied by high-precision neutron diffraction. The experiments have been performed on a high-resolution Fourier diffractometer (pulsed reactor IBR-2), which has the record resolution for the interplanar distance and a high intensity in the region of large interplanar distances; as a result, the characteristics of both transitions have been determined simultaneously. It has been shown that the structural and magnetic transitions in MnO occur synchronously and their temperatures coincide within the experimental errors: TstrTmag ≈ (119 ± 1) K. The measurements for NiO have been performed with powders with different average sizes of crystallites (~1500 nm and ~138 nm). It has been found that the transition temperatures differ by ~50 K: Tstr = (471 ± 3) K, Tmag = (523 ± 2) K. It has been argued that a unified mechanism of the “unsplit” magnetic and structural phase transition at a temperature of Tmag is implemented in MnO and NiO. Deviation from this scenario in the behavior of NiO is explained by the quantitative difference—a weak coupling between the magnetic and secondary structural order parameters.

JETP Letters. 2016;104(2):88-93
pages 88-93 views

Spin dynamics effects in submillimeter EPR spectroscopy of impurity thulium ions in synthetic forsterite

Solovarov N.K., Tarasov V.F., Zharikov E.V.

Abstract

The specific features of the EPR spectra of Tm3+ impurity ions in synthetic forsterite have been studied by continuous-wave EPR spectroscopy in the frequency range of 270–310 GHz at a temperature of 4.2 K in weak magnetic fields. Narrow resonance signals unrelated to the modulation of the resonance conditions of EPR under the modulation of the external magnetic field have been discovered in measurements at frequencies corresponding to the zero field splitting between the ground and first excited singlet electron states of Tm3+ ions in zero magnetic field. The origin of these narrow lines is discussed.

JETP Letters. 2016;104(2):94-98
pages 94-98 views

Study of the compressibility of FeSi, MnSi, and CoS2 transition-metal compounds at high pressures

Brazhkin V.V., Dzhavadov L.N., El’kin F.S.

Abstract

Silicides and sulfides of transition metals attract great attention of researchers because of a wide spectrum of interesting magnetic, electronic, and optical properties. The crystal structure of FeSi, MnSi, and CoSi silicides is P213(B20), whereas FeS2, CoS2, and MnS2 sulfides have a structure of pyrite Pa3. Despite the great interest in these systems and the cubic symmetry of crystals, the structure and compressibility of these compounds at high pressures are still insufficiently studied. There is a significant spread (more than a factor of two!) in the bulk modulus and its pressure derivative for a single compound. Most studies were performed under nonhydrostatic conditions. In this work, the compressibility of FeSi and MnSi silicides (at pressures up to 35 GPa) and CoS2 sulfide (up to 22 GPa) has been studied by the X-ray diffraction method in a diamond anvil cell with the use of helium as the softest pressure-transmitting medium. The values obtained for the bulk modulus and its derivative—B = 178 ±3 GPa and Bp = 5.6 ± 0.5 for FeSi, B = 167 ± 3 GPa and Bp' = 4.6 ± 0.5 for MnSi, and B = 94 ± 2 GPa and Bp' = 6.9 ± 0.5 for CoS2—can be considered as the most reliable and can be used to test numerous theoretical models. The results for the compressibility of FeSi are important for the verification of models of the Earth’s core.

JETP Letters. 2016;104(2):99-104
pages 99-104 views

Tunable Van Hove singularities and the magnetization in a two-dimensional electron gas with the spin–orbit interaction in a parallel magnetic field

Tkach Y.Y.

Abstract

The problem of finding the single-particle density of states of a two-dimensional electron gas with the spin–orbit interaction in a parallel magnetic field has been solved. It has been shown that, with increasing field, the square-root singularity of the density of states (N(E) ~ 1 / \(\sqrt {E + 1} \)) existing at the minimum energy in zero magnetic field becomes logarithmic (the Van Hove singularity) and is displaced inside the spectrum, and the minimum energy of the spectrum decreases. The presence of two types of spin–orbit interaction (Rashba and Dresselhaus) is responsible for two peaks of the density of states and for an additional step in the density of states at certain directions of the magnetic field. The energy position of these features can be determined from the magnetization of the electron gas. This makes it possible to find the Rashba and Dresselhaus coupling constants.

JETP Letters. 2016;104(2):105-109
pages 105-109 views

Isolated quantum emitters originating from defect centers in a ZnSe/ZnMgSSe heterostructure

Krivobok V.S., Gronin S.V., Sedova I.V., Sorokin S.V., Kozlovskii V.I., Bagaev V.S., Onishchenko E.E., Chentsov S.I., Nikolaev S.N., Ivanov S.V.

Abstract

On the basis of low-temperature (5 K) microphotoluminescence measurements in a wide ZnSe/ZnMgSSe quantum well, the existence of isolated quantum emitters in this heterostructure is demonstrated. Characteristically, the corresponding emission lines experience stepwise spectral shifts by a few meV on a time scale of 1–10 min. The unconventional properties of the observed emitters are explained by considering the picture of a system with a large dipole moment in the ground state, such as a single donor–acceptor pair or a similar system located near an extended defect.

JETP Letters. 2016;104(2):110-115
pages 110-115 views

Biophysics

Scroll wave dynamics in a model of the heterogeneous heart

Konovalov P.V., Pravdin S.F., Solovyova O.E., Panfilov A.V.

Abstract

Scroll waves are found in physical, chemical and biological systems and underlie many significant processes including life-threatening cardiac arrhythmias. The theory of scroll waves predicts scroll wave dynamics should be substantially affected by heterogeneity of cardiac tissue together with other factors including shape and anisotropy. In this study, we used our recently developed analytical model of the human ventricle to identify effects of shape, anisotropy, and regional heterogeneity of myocardium on scroll wave dynamics. We found that the main effects of apical-base heterogeneity were an increased scroll wave drift velocity and a shift towards the region of maximum action potential duration. We also found that transmural heterogeneity does not substantially affect scroll wave dynamics and only in extreme cases changes the attractor position.

JETP Letters. 2016;104(2):130-134
pages 130-134 views

Effect of the architecture of the left ventricle on the speed of the excitation wave in muscle fibers

Nezlobinsky T.V., Pravdin S.F., Katsnelson L.B., Solovyova O.E.

Abstract

It is known that preferential paths for the propagation of an electrical excitation wave in the human ventricular myocardium are associated with muscle fibers in tissue. The speed of the excitation wave along a fiber is several times higher than that across the direction of the fiber. To estimate the effect of the architecture and anisotropy of the myocardium of the left ventricle on the process of its electrical activation, we have studied the relation between the speed of the electrical excitation wave in a one-dimensional isolated myocardial fiber consisting of sequentially coupled cardiomyocytes and in an identical fiber located in the wall of a threedimensional anatomical model of the left ventricle. It has been shown that the speed of a wavefront along the fiber in the three-dimensional myocardial tissue is much higher than that in the one-dimensional fiber. The acceleration of the signal is due to the rotation of directions of fibers in the wall and to the position of the excitation wavefront with respect to the direction of this fiber. The observed phenomenon is caused by the approach of the excitable tissue with rotational anisotropy in its properties to a pseudoisotropic tissue.

JETP Letters. 2016;104(2):124-129
pages 124-129 views

Miscellaneous

Electric charge in the stochastic electric field

Simonov Y.A.

Abstract

The influence of electric stochastic fields on the relativistic charged particles is investigated in the gauge invariant path integral formalism. Using the cumulant expansion one finds the exponential relaxation of the charge Green’s function both for spinless and Dirac charges.

JETP Letters. 2016;104(2):140-143
pages 140-143 views

Optical phonon cascade emission by photoelectrons at a p-GaN (Cs,O)–vacuum interface

Rozhkov S.A., Bakin V.V., Gorshkov D.V., Kosolobov S.N., Scheibler H.E., Terekhov A.S.

Abstract

It has been experimentally established that the transfer of photoelectrons from the bulk of a p-GaN (Cs,O) photocathode to vacuum is accompanied by the emission of a cascade of optical phonons. In the quantum efficiency spectrum of the p-GaN (Cs,O) photocathode, an exciton peak has been identified, indicating a significant contribution of the electron–hole interaction to the generation of free electrons in heavily doped p-GaN.

JETP Letters. 2016;104(2):135-139
pages 135-139 views

Fields, Particles, and Nuclei

Low-energy relation for the trace of the energy–momentum tensor in QCD and the gluon condensate in a magnetic field

Agasian N.O.

Abstract

The nonperturbative QCD vacuum in a magnetic field has been studied. A low-energy relation for the trace of the energy–momentum tensor in the magnetic field has been obtained. It has been shown that the derivatives of the quark and gluon contributions to the trace of the energy–momentum tensor with respect to the magnetic field coincide with each other. The magnetic field dependence of the gluon condensate has been calculated in the limits of strong and weak fields.

JETP Letters. 2016;104(2):71-74
pages 71-74 views

Neutrino induced magnetic moment and spin precession

Ternov A.I.

Abstract

When propagating through a dispersing medium, a massive neutrino acquires an induced magnetic moment that may give rise to a helicity flip in an external magnetic field with a larger probability than that caused by the anomalous magnetic moment. This phenomenon is investigated in the framework of relativistic quantum mechanics and of the generalized Bargmann–Michel–Telegdi equation.

JETP Letters. 2016;104(2):75-81
pages 75-81 views